Field of the Invention
The present invention relates to an optical biological measuring device using light and analysis method for acquiring an observation signal indicating time-course (chronological) variations in terms of a measurement site. Particularly, the present invention is used as an optical cerebral function imaging apparatus for measuring an activity situation of a cerebral measurement site in a noninvasive manner using near-infrared rays, and an oxygen monitor for monitoring oxygen consumption in a measurement site in a living body.
Description of the Related Art
In recent years, in order to observe a cerebral activity situation, optical cerebral function imaging apparatuses for conducting a measurement in a simple and noninvasive manner using light have been developed. In such optical cerebral function imaging apparatuses, the brain is irradiated with near infrared rays with three different wavelengths of λ1, λ2 and λ3 (for example, 780 nm, 805 nm and 830 nm) from a light transmission probe arranged on the scalp surface of a subject, and intensity variations (information of an amount of received light) ΔA(λ1), ΔA(λ2) and ΔA(λ3) of the near infrared rays with wavelengths of λ1, λ2 and λ3 emitted from the brain are detected by light reception probes arranged on the scalp surface.
In order to obtain a product [oxyHb] of oxyhemoglobin concentration change and optical path length and a product [deoxyHb] of deoxyhemoglobin concentration change and optical path length in the cerebral blood flow from ΔA(λ1), ΔA(λ2), ΔA(λ3), the information of the amount of received light obtained in this manner, for example, simultaneous equations shown by the relational equations (1), (2) and (3) are formulated by using, for example, Modified Beer Lambert Law, and then the simultaneous equations are solved. Further, a product ([oxyHb]+[deoxyHb]) of total hemoglobin concentration change and optical path length is calculated from the product [oxyHb] of oxyhemoglobin concentration change and optical path length and the product [deoxyHb] of deoxyhemoglobin concentration change and optical path length.ΔA(λ1)=EO(λ1)×[oxyHb]+Ed(λ1)×[deoxyHb]  (1)ΔA(λ2)=EO(λ2)×[oxyHb]+Ed(λ2)×[deoxyHb]  (2)ΔA(λ3)=EO(λ3)×[oxyHb]+Ed(λ3)×[deoxyHb]  (3)
EO (λm) represents an absorbance coefficient of oxyhemoglobin at the light with wavelength λm, and Ed(λm) represents an absorbance coefficient of deoxyhemoglobin at the light with wavelength λm.
Here, a relationship between distance (channel) between the light transmission probe and the light reception probe and a measurement site is described. FIGS. 8A and 8B are diagrams illustrating a relationship between a pair of a light transmission probe and a light reception probe and a measurement site. A light transmission probe 12 is pressed against a light transmitting point T of the scalp surface of a subject, and a light reception probe 13 is pressed against a light receiving point R of the scalp surface of the subject. Light is irradiated from the light transmission probe 12, and then light emitted from the scalp surface is incident on the light reception probe 13. At this time, light that is radiated and passes through a banana-like shape region (measurement region) of the light radiated from the light transmitting point T of the scalp surface reaches the light receiving point R of the scalp surface.
Further, in the optical cerebral function imaging apparatuses, for example, a near-infrared spectrometer is used in order to measure the product [oxyHb] of oxyhemoglobin concentration change and optical path length, the product [deoxyHb] of deoxyhemoglobin concentration change and optical path length, and the product ([oxyHb]+[deoxyHb]) of total hemoglobin concentration change and optical path length related to a plurality of measurement sites in the brain.
In such a near-infrared spectrometer, a holder (transmission/reception portion) 130 is used in order to allow the eight light transmission probes 12 and the eight light reception probes 13 to contact with the scalp surface of a subject in a predetermined arrangement. FIG. 9 is a plan diagram illustrating one example of the holder 130 into which the eight light transmission probes and the eight light reception probes are inserted.
Light transmission probes 12T1 to 12T8 and light reception probes 13R1 to 13R8 are alternately arranged to make four in the vertical direction and the horizontal direction. At this time, a second setting distance r2 that is an interval (channel) between each of the light transmission probes 12T1 to 12T8 and each of the light reception probes 13R1 to 13R8 is 30 mm. As a result, the information of the amount of received light ΔA2n(λ1), ΔA2n(λ2) and ΔA2n(λ3) (n=1, 2, . . . , 24) concerning twenty-four measurement positions of the brain are obtained.
The twenty-four information of the amount of received light ΔA2n(λ1), ΔA2n(λ2) and ΔA2n(λ3) are obtained at a predetermined time interval Δt so that time-course (chronological) variations (second observation signal) Xn(t) of the product [oxyHb] of oxyhemoglobin concentration change and optical path length, time-course variations (second observation signal) Yn(t) of the [deoxyHb] of deoxyhemoglobin concentration change and optical path length, and time-course variations (second observation signal) Zn(t) of the product ([oxyHb]+[deoxyHb]) of total hemoglobin concentration change and optical path length (n=1, 2, . . . , 24) are obtained by using the relational equations (1), (2) and (3).
FIG. 5 is a diagram illustrating a monitor screen where twenty-four time-course variations (second observation signals) Xn(t) of the product [oxyHb] of oxyhemoglobin concentration change and optical path length are being displayed. Further, the vertical axis in one of second observation signal Xn(t) represents the product [oxyHb] of oxyhemoglobin concentration change and optical path length, and the horizontal axis represents time t.
Incidentally, as shown in FIG. 5, the displayed twenty-four of second observation signals Xn(t) include overlapping signals based on the fluctuations in the blood flow in the skin, the heart rate, variations in pulsation and respiration and so forth, in addition to signals based on the blood flow according to the brain activity.
Therefore, in order to easily diagnose whether or not symptoms such as cerebral ischemia are generated, a biological light measuring method for surely discriminating the signals based on the blood flow according to the brain activity from signals other than these signals in the second observation signal Xn(t) is disclosed (for example, see Patent Document 1). Such a biological light measuring method includes a step (a) of obtaining an N×N mixing matrix and numerical N independent component signals Sn (t) based on observation signals Xn(t) on numerical N detection positions through independent component analysis (ICA) according to the following formula (4); a step (b) of substituting 0 for a column vector corresponding to a removal target component in the N×N mixing matrix as expressed in the following formula (5); and a step (c) of calculating a product of the N×N removal target component removal mixing matrix and numerical N independent component signals Sn(t) so as to obtain numerical N removal target component removal observation signals Xn′(t).
                    [                  Mathematical          ⁢                                          ⁢          Formula          ⁢                                          ⁢          1                ]                                                                                  (                                                                                                      X                      1                                        ⁡                                          (                      t                      )                                                                                                                                                              X                      2                                        ⁡                                          (                      t                      )                                                                                                                    ⋮                                                                                                                        X                      n                                        ⁡                                          (                      t                      )                                                                                            )                                                              observation                                                                    signal                                                    =                                            (                                                                                          a                      11                                                                                                  a                      12                                                                            …                                                                              a                                              1                        ⁢                        n                                                                                                                                                        a                      21                                                                                                  a                      12                                                                            …                                                                              a                                              2                        ⁢                        n                                                                                                                                  ⋮                                                                                                                                                  ⁢                      ⋮                                                                            ⋱                                                        ⋮                                                                                                              a                                              n                        ⁢                                                                                                  ⁢                        1                                                                                                                        a                                              n                        ⁢                                                                                                  ⁢                        2                                                                                                                        …                      ⁢                                                                                                                                                                      a                      nn                                                                                  )                                      mixing              ⁢                                                          ⁢              matrix                                ⁢                                    (                                                                                                                  S                        1                                            ⁡                                              (                        t                        )                                                                                                                                                                                S                        2                                            ⁡                                              (                        t                        )                                                                                                                                  ⋮                                                                                                                                      S                        n                                            ⁡                                              (                        t                        )                                                                                                        )                                                                        independent                                                                                                  component                    ⁢                                                                                  ⁢                    signal                                                                                                          (        4        )            
The column vector in the mixing matrix represents a weight of a specific independent component signal Sn(t) in a measurement site. That is to say, the observation signals Xn(t) are a linear combination of numerical N independent component signals Sn(t) from independent signal generating sources with respective elements in the mixing matrix as a weight coefficient.
                    [                  Mathematical          ⁢                                          ⁢          Formula          ⁢                                          ⁢          2                ]                                                                                  (                                                                                                      X                      1                      ′                                        ⁡                                          (                      t                      )                                                                                                                                                              X                      2                      ′                                        ⁡                                          (                      t                      )                                                                                                                    ⋮                                                                                                                        X                      n                      ′                                        ⁡                                          (                      t                      )                                                                                            )                                                                                Removal                  ⁢                                                                          ⁢                  target                                                                                    component                                                                    removal                                                                                      observation                  ⁢                                                                          ⁢                  signal                                                                    =                                            (                                                                    0                                                                              a                      12                                                                            …                                                                              a                                              1                        ⁢                        n                                                                                                                                  0                                                                              a                      12                                                                            …                                                                              a                                              2                        ⁢                        n                                                                                                                                  0                                                                                                                                                  ⁢                      ⋮                                                                            ⋱                                                        ⋮                                                                                        0                                                                              a                                              n                        ⁢                                                                                                  ⁢                        2                                                                                                                        …                      ⁢                                                                                                                                                                      a                      nn                                                                                  )                                                                                            Removal                                                                                                              target                      ⁢                                                                                          ⁢                      component                                                                                                            removal                                                                                                              mixing                      ⁢                                                                                          ⁢                      matrix                                                                                  ⁢                                                                            ⁢                                    (                                                                                                                  S                        1                                            ⁡                                              (                        t                        )                                                                                                                                                                                S                        2                                            ⁡                                              (                        t                        )                                                                                                                                  ⋮                                                                                                                                      S                        s                                            ⁡                                              (                        t                        )                                                                                                        )                                                                                            I                    ⁢                    ndependent                                                                                                                    component                    ⁢                                                                                  ⁢                    signal                                                                                                          (        5        )            
The expression (5) shows a case where an independent component signal S1(t) is determined as a removal target component, 0 is substituted for a first column vector corresponding to the removal target component, and a removal target component removal mixing matrix is generated.
According to such a biological light measuring method, the removal target component removal observation signals Xn′(t) can be restored, in which the signal S1(t) based on the removal target component from the observation signals Xn(t) is removed.
On the other hand, in order to acquire the information of the amount of received light ΔA only based on a blood vessel in the brain, that having a distance (channel) between the light transmission probe 12 and the light reception probe 13 is set as both a short distance r1 and a long distance r2 is disclosed (for example, see Patent Document 2 and Non-Patent Document 1.) FIG. 10 is a cross-sectional diagram illustrating a relationship between the light transmission probe 12 to make a short distance r1 with a reference probe 14 and a long distance r2 with the light reception probe 13 and a measurement site. As a result, second information of the amount of received light ΔA2 about a blood vessel present in the skin near the light transmitting point T, a blood vessel present in the brain and a blood vessel present in the skin in proximity to the light receiving point R2 is acquired at the long distance r2 channel, and first information of the amount of received light ΔA1 about only a blood vessel present in the skin in proximity to the light transmitting point T (blood vessel present in the skin in proximity to a light receiving point R1) is acquired at the short distance r1 channel.
The information of the amount of received light ΔA about only the blood vessel present in the brain is obtained based on the information of the amount of received light ΔA1 and ΔA2 by using the equation (6).ΔA=ΔA2−KΔA1  (6)
Incidentally, in the equation (6), a coefficient K should be determined in order to obtain the information of the amount of received light ΔA, and a method for calculating the coefficient K is disclosed (for example, see Non-Patent Document 2.) In this calculating method, the coefficient K is calculated by using least square error.